Time division multiple access (TCMA) systems are being developed for digital mobile and portable radio systems. These TDMA systems can greatly simplify radio hardware and can accommodate variable user data rates.
However, such systems become inefficient when there is a large number of overhead symbols required to synchronize symbol timing. The large number of symbols will often result in a significant reduction in spectral efficiency, nullifying the advantages obtained with the use of TDMA.
The present invention uses a new and elegant digital signal processing technique for obtaining symbol timing. The technique of the invention is completely digital resulting in circuitry that is greatly simplified and which lends itself to low-power VLSI implementation.
The inventive technique allows for the demodulation of isolated bursts on the order of 100 symbols in length with no overhead penalty for symbol timing, frequency estimation or coherent carrier recovery.
The invention eliminates the requirement for multiplication in the processing of the data.
Frequency offset estimation is uniquely fed forward to the carrier recovery phase of the processing.
Differential detection is also available within the scope of the invention, thus providing the unique opportunity to switch to the differential mode if the receiver is used in a fast-fading condition where coherent phase recovery becomes more difficult.